This invention relates to a poppet for a center port valve located in a bore of a master cylinder to control communication between the bore and a reservoir.
U.S. Pat. Nos. 5,018,353 and 5,111,661 disclose master cylinders wherein compensation between a first chamber in a bore of a housing and a reservoir occurs through a single center port compensation valve associate with a first piston and between a second chamber in the bore through a relationship established between a radial port and sealing structure carried on a second piston. In order to eliminate the possibility of cutting a nub in a seal by extrusion into the radial port, U.S. Pat. Nos. 5,207,062; 5,279,125 and 5,943,863 disclose the use of a second center port compensation valve through which compensation is achieved for the second operational chamber in a bore. Most such master cylinders have a separate compensation valve for the first and second pressurizing chambers in the bore through which communication typically occurs through ports when the first and second pistons are in a rest position. As the first and second pistons approach the rest position, a stop pin engages the compensation valve to open the compensation valve and initiate communication between the bore and reservoir. Unfortunately, the passage required to connect the rear chamber is quite long as the compensation port needs to be located adjacent the end of the housing of the master cylinder. In addition, when such master cylinders are recessed into a front chamber of a vacuum brake booster care needs to be taken with respect to sealing structure to assure that vacuum does not draw fluid into the vacuum brake booster. While this type master cylinder functions in an adequate manner under some circumstances, the fluid pressure generated during a brake application may extrude a portion of a poppet into a compensation port leading to a reservoir and as a result it may be possible to cut the face on the poppet to an extent that a leak may develop between the bore and the reservoir during a brake application.
A primary object of the present invention is to provide a brake system with a valve arrangement whereby a face on a poppet engages a sealing surface without being extruded into a compensation port during a brake application.
According to this invention, a brake system is equipped with a master cylinder having a housing with a bore that is connected through axial port in the bottom of the bore and a radial port with a reservoir and to the brake system through first and second outlet ports. First and second pistons are positioned in the bore by a first resilient means located between the first and second pistons to define limits for a first chamber and by a second resilient means located between the second piston and the bottom of the bore to define limits for a second chamber. The first and second resilient means each include a first spring and a second spring with the first spring caged between a first retainer and a second retainer to define a linkage member. The linkage member has a stem with a head that engages the first retainer and an end that is screwed into a poppet member that is concentrically located in the second retainer. The second spring is located between the head and the second retainer member. The first chamber is connected to the radial port through an axial passage in the second piston while the second chamber is connected to the axial port in the housing. The first and second pistons respond to an input force applied to the first piston by initially moving within the bore to compress the first springs of the first and second resilient means and allow the second springs to simultaneously move the poppet associated with the first resilient means into engagement with the axial passage or port into the second piston and the poppet associated with the second resilient means into engagement with the axial port into engagement with the housing to terminate communication between the bore and the reservoir. Further movement of the first and second pistons by the input force pressurizes fluid in the first and second chambers that is provided to the brake system through the first and second outlet ports for effecting a brake application. As the poppets come into respective engagement the second piston and bottom of the housing, a lip on a resilient ring located in an axial projection of a cylindrical body initially engages a seat in an annular point contact to interrupt communication between the bore and the reservoir and as the fluid pressure develops in the first and second chambers, the fluid pressure and the second springs urge the cylindrical body toward the seat as the resilient ring is compressed with the lip being radially extruded such that when the face on the cylindrical body engages the seat, the compression of the resilient ring ends and a sealing engagement extends along a substantially length of the lip to seal the bore from the reservoir.
An advantage of this brake system is provided by utilizing a head attached to a stem of a linkage component that cages a spring as a poppet for a compensation valve to control communication between a reservoir and the bore of a master cylinder.
A still further advantage of this invention is provided by utilizing a cylindrical body of a head for a caging arrangement as a poppet for a compensation valve wherein a resilient member retained on an axial projection that extends from the cylindrical body has a lip that engages a seat as the cylindrical body is moved toward a seat and the resilient member is compressed such that once the axial projection engages the seat the lip will have been radially extruded and a sealing surface extended from an annular point contact to substantially an entire face of the lip.